**3. Mechanism of "slumping method"**

The "slumping method" was proposed for the manufacture of the base shape of super mirrors and other optical components. The slumping method is a glass forming process with heating at the glass softening point [12]. **Figure 2** presents an overview of the "slumping method". A glass plate is placed on a molding die that has the shape of the optical component. The glass plate is then heated and thermoformed along the molding die. The surface roughness of the molding die is critical because it may be transcribed to the glass surface if it is rough. Therefore, high-precision polishing of the molding die should be performed to achieve a highly precise surface roughness. In addition, the molding die must also exhibit good heat resistance to enable its exposure to repeated heating processes.
